In telecommunications equipment such as cross-connects, it is desirable for some applications to process a high number of high speed signals on a single circuit card. If many high speed signals can be processed by a single circuit card with reasonable power consumption and at reasonable cost, then the overall cost of the telecommunications switching equipment per channel may be reduced. Thus, in recent years, telecommunications equipment manufacturers have attempted to achieve higher density processing of telecommunications signals. Higher density processing allows more high speed telecommunication signals to be processed on a circuit board of a given size than was previously possible.
Many high speed telecommunications signals such as T1 or DS1 signals include a facility datalink signal. Facility datalink signals in a T1 or DS1 are typically four kilobit per second channels that are used for performance monitoring and high priority system messages between various pieces of telecommunication switching equipment. Facility datalink signals include HDLC formatted messages including 54016 messaging signals. Such signals are typically 14 byte signals comprising 8 data bytes, 2 address bytes, 2 CRC error correction code bytes, 1 byte of flag information, and 1 byte of control information. Such messages are sometimes referred to as PRM messages (performance report messages). Facility datalink signals may also use high priority messages known as BOM messages (bit oriented messages) which may contain a 1 byte abort signal and a 1 byte code message.
DS3 or T3 signals typically include 28 DS1s or 28 T1 signals, respectively. Because each DS1 or T1 typically includes a facility datalink signal, processing a DS3 or T3 signal will also require the processing of 28 individual facility datalink signals. Producing high density circuit cards to process multiple facility datalinks thus presents a problem. The use of multiple integrated circuits each capable of processing only a single facility datalink may be impractical due to space on the printed circuit board, the cost of the integrated circuits and their power consumption.
One technique that can be used to process multiple versions of a communications signal with the same integrated circuit is to employ a state machine capable of processing one channel that is shared among multiple channels. Of course, such a circuit must operate fast enough to process all of the channels simultaneously. There is a trade-off between speed and the amount of circuitry required to process multiple signals simultaneously. Existing shared state machines will often load and unload the state associated with a particular channel in a round-robin fashion. Such loading and unloading of state information, however, may be inefficient if the signal does not need to be processed at the time that its state is loaded into the shared state machine.
In processing multiple communication channels, it is sometimes unnecessary to process certain signals on an ongoing basis. Performance monitoring information and error messages such as are provided by facility datalink signals may be received infrequently and at varying time intervals. Thus, it is desirable to interrupt a microprocessor controlling the system to process a facility datalink signal only when such a signal indicates that some intelligent processing is required by the telecommunications equipment. Efficiently interrupting the microprocessor may become difficult, however, when a large number of facility datalink signals are processed simultaneously. Thus, a novel method of alerting a processor that a particular datalink needs to be processed is needed.